1. Field of the Invention
The present invention relates to a method of protecting a second pole tip thickness during fabrication of a write head and, more particularly, to preventing a reduction in the thickness of the second pole tip during subsequent processing steps, such as seed layer removal, sputter cleaning the wafer and formation of studs for terminals.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
A write head typically employs ferromagnetic first and second pole pieces which are capable of carrying flux signals for the purpose of writing magnetic impressions into a track on a magnetic medium, such as a rotating magnetic disk. Each of the first and second pole pieces has a yoke region which is located between a pole tip region and a back gap region. The pole tip region is located at the ABS and the back gap region is spaced from the pole tip region at a recessed location within the write head. At least one coil layer is embedded in an insulation stack which is located between the first and second pole pieces in the yoke region. A nonmagnetic write gap layer is located between the pole tip regions of the first and second pole pieces. The thinner the thickness of the write gap layer, the greater the number of bits the write head can write into the track of a rotating magnetic disk. The first and second pole pieces are magnetically connected at the back gap. Processing circuitry digitally energizes the write coil which induces flux into the first and second pole pieces so that flux signals bridge across the write gap at the ABS to write the aforementioned magnetic impressions or bits into the track of the rotating disk. The second pole piece has a second pole piece yoke (P2 yoke) which is magnetically connected to the second pole tip (P2 tip) and extends to the back gap for connection to the first pole piece.
A write head is typically rated by its areal density which is a product of its linear bit density and its track width density. The linear bit density is the number of bits which can be written per linear inch along the track of a rotating magnetic disk and the track width density is the number of tracks that can be written per inch along a radius of the rotating magnetic disk. The linear bit density is quantified as bits per inch (BPI) and the track width density is quantified as tracks per inch (TPI). As discussed hereinabove, the linear bit density depends upon the thickness of the write gap layer. The track width density is directly dependent upon the width of the second pole tip at the ABS. Efforts over the years to increase the areal density of write heads has resulted in computer storage capacities increasing from kilobytes to megabytes to gigabytes.
The first and second pole pieces, including the second pole tip, are typically fabricated by plating techniques. The strong-felt need to fabricate second pole tips with submicron widths is limited by the resolution of the fabrication techniques. The second pole tip is typically fabricated by frame plating. Photoresist is employed to provide the frame and a seed layer is employed to provide a return path for the plating operation. A typical sequence for fabricating a second pole tip, as well as other components of the first and second pole pieces, is to sputter clean the wafer, sputter deposit a seed layer, such as nickel iron, on the wafer, spin a layer of photoresist on the wafer, light-image the photoresist layer through a mask to expose areas of the photoresist that are to be removed (assuming that the photoresist is a positive photoresist), develop the photoresist to remove the light-exposed areas to provide an opening in the photoresist at the pole tip region and then plate the second pole tip in the opening up to a desired height.
It is necessary that a second pole tip have a sufficient amount of volume at the ABS in order to conduct the required amount of flux for writing the signals into the magnetic disk. If the second pole tip is made thinner, it must be made higher in order to provide the necessary volume of magnetic material. Unfortunately, as the track width becomes narrower the resolution of the photoresist decreases. Resolution is quantified as aspect ratio which is the width of the second pole tip versus the thickness of the photoresist. As the thickness of the photoresist increases the light penetration during the light-imaging step loses its columnation as it travels toward the bottom of the photoresist. The result is that the side walls of the photoresist frame are jagged which results in jagged side walls of the second pole tip.
The aforementioned problems are particularly manifested when the second pole tip and the yoke of the second pole piece are plated simultaneously in a common photoresist frame. In addition to loss of resolution with an increasing height of the second pole tip, there is also notching of the side walls of the photoresist frame, and consequently the second pole tip, due to reflection of light from a seed layer on the insulation stack immediately behind the pole tip region. One method to overcome this problem has been to employ a stitched xe2x80x9cTxe2x80x9d-shaped second pole piece which is fabricated by first making only the second pole tip portion with a photoresist frame and then subsequently making the yoke portion of the second pole piece with a second photoresist frame with the yoke portion being stitched (magnetically connected) to a stitch region at the top of the second pole tip. This type of second pole piece is referred to as a stitched xe2x80x9cTxe2x80x9d because the yoke portion extends laterally across the top of the pole tip portion, forming the configuration of a xe2x80x9cTxe2x80x9d. The yoke portion can be stitched across the entire top surface of the second pole tip in which case it is exposed at the ABS or it may be recessed from the ABS, as desired.
Unfortunately, processing steps subsequent to the construction of the second pole tip decrease the height of the second pole tip and can seriously damage its side walls. When the second pole piece is a continuous pole tip and yoke combination these processing steps are removal of the seed layer by sputter etching after removal of the photoresist frame and the fabrication of studs for write head and read head terminals which involves sputter etching to clean the wafer, depositing a seed layer, photoresist framing the areas involved, plating the studs, removing the photoresist layer and sputter etching the exposed seed layer. While these steps lessen the height of the second pole tip of the continuous second pole tip and yoke combination, it is even more aggravated with the stitched xe2x80x9cTxe2x80x9d type of second pole piece. After the second pole tip of the stitched xe2x80x9cTxe2x80x9d is fabricated, sputter etching is required to remove the seed layer employed to fabricate the pole tip which further reduces the height of the second pole tip. Further, if chemical mechanical polishing (CMP) is employed for planarizing the wafer, preparation steps for this operation can further reduce the height of the second pole tip.
In order to overcome the loss of height of the second pole tip while maintaining a narrow track width (width of the second pole tip) the second pole tip can be frame plated to a greater height so that after the processing steps the remaining height of the second pole tip is at a desired level. Unfortunately, this requires the photoresist frames to be thicker which increases the aforementioned aspect ratio. Consequently, the resolution of the photoresist frame is lessened which degrades the resolution of the finally plated second pole tip.
The present invention provides a stitched xe2x80x9cTxe2x80x9d type of second pole piece wherein the second pole tip portion is protected from a reduction in height due after subsequent processing steps. In the present invention the top surface of the second pole tip has a write region which is located at the ABS and a stitch region which is recessed from the ABS toward the back gap. A protective sacrificial layer is deposited on the write region of the second pole tip and the second pole piece yoke is magnetically connected to the stitch region. The method includes first depositing the sacrificial layer on both the write region and the stitch region of the second pole tip. The sacrificial layer is then removed from only the stitch region of the second pole tip leaving a portion of the sacrificial layer covering the write region of the second pole tip.
Several methods are employed for accomplishing these steps. In a first embodiment, the sacrificial layer is deposited over the entire wafer. The sacrificial layer is then chemically mechanically polished (CMP) until it is flat, but stopping the CMP before the top surface of the second pole tip is exposed, and then before forming the second pole piece yoke, removing the sacrificial layer from only the stitch region by sputter etching or ion milling until the stitch region is exposed. The second pole piece yoke is then stitched to the exposed stitch region of the second pole tip. In another embodiment the second pole tip is provided with an upstanding pedestal which is located in the stitch region. Again the sacrificial layer is deposited over the entire wafer, the sacrificial layer is then chemically mechanically polished until it is flat and until the pole tip pedestal in the stitch region is exposed, but stopping the chemical mechanical polishing before the write region of the second pole tip is exposed. The second pole piece yoke is then magnetically connected to the second pole tip pedestal. The invention provides a unique method of obtaining the second pole tip pedestal by forming an insulation layer directly below the second pole tip before its formation and then forming a second pole tip so that the profile of the insulation layer forms the second pole tip with the pedestal.
In a preferred embodiment of the invention the write head employs first and second coil layers which are embedded in first and second insulation stacks which are stacked on top of each other. This is accomplished by providing the first pole piece with a first pole piece layer and first and second spaced-apart pedestals which are magnetically connected to the first pole piece layer. The first pedestal is located at the ABS and the second pedestal is located at the back gap. The first insulation stack with the first write coil embedded therein is located in the space between the first and second pedestals and is separated from the first pole piece layer by a first insulation layer. The write gap layer is located on the first pedestal and may extend all the way from the ABS to the back gap. The second pole piece includes the second pole tip portion at the ABS and a back gap pedestal at the back gap with a yoke portion extending between the second pole tip and the back gap pedestal and magnetically connected thereto. The second pole tip is separated from the first pedestal of the first pole piece by the write gap layer. The second insulation stack with the write coil embedded therein is located between the second pole tip and the back gap pedestal and may be separated or further separated from the first write coil by a second insulation layer. The sacrificial layer is then formed over the entire wafer and the stitch region of the second pole tip is exposed by one of the methods described hereinabove followed by fabrication of the second pole piece yoke. In a preferred embodiment, the aforementioned first insulation layer, the second insulation layer and the sacrificial layer are chemically mechanically polished (CMP). Further, the composition of each of the first and second insulation layers and the sacrificial layer is preferably alumina.
An object of the present invention is to protect a pole tip portion of a second pole tip in a stitched xe2x80x9cTxe2x80x9d second pole piece from subsequent processing steps.
Another object is to provide unique methods for exposing a stitch region of the second pole tip for stitching a yoke portion of a second pole piece thereto.
A further object is to accomplish the aforementioned objects with first and second insulation stacks with first and second write coils embedded therein.
Still another object is to provide the various write heads fabricated by the aforementioned methods.
Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings.